Japanese Patent No. 5255063 discloses a sleepiness sign detection device aiming at detecting a sign before a driver of a vehicle feels sleepiness using vestibulo-ocular reflex induced by a head movement.
The sleepiness sign detection device of Japanese Patent No. 5255063 includes a head movement detection unit for detecting head movement, an eye movement detection unit for detecting eye movement, an ideal eye movement angular velocity calculation unit for calculating ideal eye movement angular velocity based on head movement data detected by the head movement detection unit, an eye rotation angular velocity calculation unit for calculating eye rotation angular velocity based on eye movement data detected by the eye movement detection unit, and a sleepiness sign determination unit for detecting Vestibulo-Ocular Reflex (VOR) from the ideal eye movement angular velocity and the eye rotation angular velocity and determining a sign of sleepiness based on the vestibulo-ocular reflex.
Japanese Patent No. 5255063 discloses a result in which a test is conducted while an experimental task such as fixation of an upper portion of a license plate of the preceding vehicle projected on a screen as a fixation point is imposed on a subject using an experimental system simulating a driving time of a vehicle, namely, a driving simulator system.
However, the pseudo experimental environment using the driving simulator system is greatly different from an actual running environment of the vehicle. The inventor has found that, as a result of verification in the actual running environment of the vehicle (hereinafter, referred to as an actual vehicle environment), a vestibulo-ocular reflex movement is hardly accurately acquired in the actual vehicle environment.
Examples of the eye movements include a saccadic movement (also referred to as an impulsive eye movement) and a congestion movement in addition to the vestibulo-ocular reflex movement. In the experimental environment, the predetermined fixation point is fixated such that the vestibulo-ocular reflex movement is easily generated. However, in the actual vehicle environment, a situation outside the vehicle, a situation of a road surface, a behavior of the vehicle, and the movement of the driver's head and eyes are not constant, and the eye movements other than the vestibulo-ocular reflex movement are generated in a complex manner.
The vestibulo-ocular reflex movement is induced by the head movement. In the experimental environment, the driver's seat is vibrated to induce the head movement. However, in the actual vehicle environment, a vibration state in which the head movement is induced is not necessarily generated. Therefore, it is difficult to determine the sleepiness with high accuracy even if the sleepiness is to be determined based on the vestibulo-ocular reflex movement in the situation in which various types of eye movements are generated or the situation in which the vestibulo-ocular reflex movement is hardly induced. In addition to the actual vehicle environment, the similar problem may be generated even in various real environments such as an operation environment or a work environment of equipment.